A cardiopulmonary bypass circuit (i.e., a heart-lung bypass machine) mechanically pumps a patient's blood and oxygenates the blood during major surgery. Blood oxygenators are disposable components of heart-lung bypass machines used to oxygenate blood. A typical commercially available blood oxygenator integrates a heat exchanger with a membrane-type oxygenator.
Typically, in a blood oxygenator, a patient's blood is continuously pumped through the heat exchanger portion prior to the oxygenator portion. A suitable heat transfer fluid, such as water, is pumped through the heat exchanger, separate from the blood but in heat transfer relationship therewith. The water is either heated or cooled externally of the heat exchanger. The heat exchanger is generally made of a metal or a plastic, which is able to transfer heat effectively to blood coming into contact with the metal or plastic. After blood contacts the heat exchanger, the blood then typically flows into the oxygenator.
The oxygenator generally comprises a so-called “bundle” of thousands of tiny hollow fibers typically made of a special polymeric material having microscopic pores. The blood exiting the heat exchanger then flows around the outside surfaces of the fibers of the oxygenator. At the same time, an oxygen-rich gas mixture, sometimes including anesthetic agents, flows through the hollow fibers. Due to the relatively high concentration of carbon dioxide in the blood arriving from the patient, carbon dioxide from the blood diffuses through the microscopic pores in the fibers and into the gas mixture. Due to the relatively low concentration of oxygen in the blood arriving from the patient, oxygen from the gas mixture in the fibers diffuses through the microscopic pores and into the blood. The oxygen content of the blood is thereby raised, and its carbon dioxide content is reduced.
An oxygenator must have a sufficient volumetric flow rate to allow proper temperature control and oxygenation of blood. A disadvantage of perfusion devices incorporating such oxygenators is that the priming volume of blood is large. Having such a large volume of blood outside of the patient's body at one time acts to dilute the patient's own blood supply. Thus, the need for a high prime volume of blood in an oxygenator is contrary to the best interest of the patient who is undergoing surgery and is in need of a maximum possible amount of fully oxygenated blood in his or her body at any given time. This is especially true for small adult, pediatric and infant patients. As such, hemoconcentration of the patient and a significant amount of additional blood, or both, may be required to support the patient. Therefore, it is desirable to minimize the prime volume of blood necessary within the extracorporeal circuit, and preferably to less than 500 cubic centimeters. One way to minimize the prime volume is to reduce the volume of the blood oxygenator. There are limits to how small the oxygenator can be made, however, because of the need for adequate oxygen transfer to the blood, which depends in part on a sufficient blood/membrane interface area.
The cells (e.g., red blood cells, white blood cells, platelets) in human blood are delicate and can be traumatized if subjected to shear forces. Therefore, the blood flow velocity inside a blood oxygenator must not be excessive. The configuration and geometry, along with required velocities of the blood make some perfusion devices traumatic to the blood and unsafe. In addition, the devices may create re-circulations (eddies) or stagnant areas that can lead to clotting. Thus, the configuration and geometry of the inlet port, manifolds and outlet port for a blood flow path is desired to not create re-circulations (eddies), while also eliminating stagnant areas that can lead to blood clot production.
Overall, there is a need for improved components of cardiopulmonary bypass circuits. Such improved components will preferably address earlier problematic design issues, as well as be effective at oxygenating and controlling the temperature of blood.